Liquid crystal display device, polarizer and protective film

ABSTRACT

Provided is a liquid crystal display device that has excellent visibility while using a protective film comprising a polyester film. The liquid crystal display device comprises a backlight light source, and a liquid crystal cell disposed between two polarizers; the backlight light source being a white light-emitting diode; each of the polarizers comprising a polarizing film and protective films laminated on both sides of the polarizing film; and at least one of the protective films being a polyester film having a retardation of 3,000 to 30,000 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of copending U.S. patentapplication Ser. No. 15/476,339, filed on Mar. 31, 2017, which is acontinuation of U.S. patent application Ser. No. 13/806,023, filed onDec. 20, 2012, now U.S. Pat. No. 9,798,189, issued on Oct. 24, 2017,which is the U.S. national phase of International Patent Application No.PCT/JP2011/064026, filed Jun. 20, 2011, which claims the benefit ofJapanese Patent Application No. 2011-111442, filed on May 18, 2011, andJapanese Patent Application No. 2010-141249, filed on Jun. 22, 2010,which are incorporated by reference in their entireties herein.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device, apolarizer (polarizing plate), and a protective film. More specifically,the present invention relates to a liquid crystal display device, apolarizer, and a protective film, all of which ensure high visibilityand are suitable for thinner liquid crystal display devices.

BACKGROUND ART

Polarizers used in liquid crystal display devices (LCDs) generally havea structure in which a polarizing film obtained by dyeing polyvinylalcohol (PVA), etc., with iodine is sandwiched between two protectivefilms. Triacetyl cellulose (TAC) films are commonly used as theprotective films. Along with the recent trend of thinner LCDs, there isa demand for reducing the thickness of polarizers. However, when thethickness of TAC films used as protective films is reduced in order tosatisfy this demand, problems such as insufficient mechanical strengthand deteriorated moisture permeability occur. Moreover, TAC films arevery expensive, and inexpensive alternative materials are stronglydesired.

Accordingly, in order to reduce the thickness of polarizers, there is aproposal to use polyester films as protective films in place of TACfilms, so that high durability can be maintained even though thethickness of the films is low (PTL 1 to PTL 3).

CITATION LIST Patent Literature PTL 1: Japanese Unexamined PatentPublication No. 2002-116320 PTL 2: Japanese Unexamined PatentPublication No. 2004-219620 PTL 3: Japanese Unexamined PatentPublication No. 2004-205773 SUMMARY OF INVENTION Technical Problem

Polyester films are superior in durability to TAC films; however, unlikeTAC films, polyester films have birefringence. Therefore, the use ofpolyester films as protective films causes problematic lower imagequality due to optical distortion. That is, polyester films havingbirefringence have a specific optical anisotropy (retardation);therefore, when they are used as protective films, rainbow unevenness isobserved from an oblique direction, and image quality deteriorates.Hence, PTL 1 to PTL 3 attempt to reduce the retardation by usingcopolymerized polyester as the polyester. However, even such an attemptfailed to completely prevent rainbow unevenness.

The present invention was made to solve these problems. An object of thepresent invention is to provide a liquid crystal display device and aprotective film, both of which can be used for thinner liquid crystaldisplay devices (that is, they have sufficient mechanical strength) anddo not have reduced visibility due to rainbow unevenness.

Solution to Problem

The present inventors conducted intensive studies on the mechanism ofrainbow unevenness that occurs when using a polyester film as aprotective film. The results revealed that the rainbow unevenness wasattributable to the retardation of the polyester film and the emissionspectrum of the backlight light source. Conventionally, fluorescenttubes, such as cold-cathode tubes and hot-cathode tubes, are used asbacklight light sources of liquid crystal display devices. The spectraldistribution of fluorescent lamps, such as cold-cathode tubes andhot-cathode tubes, shows emission spectra having a plurality of peaks.These discontinuous emission spectra are combined to provide a whitelight source. When a film having a high retardation transmits light,transmission intensity varies depending on the wavelength of the light.Accordingly, when the backlight light source has discontinuous emissionspectra, only light of a specific wavelength is intensively transmitted,presumably leading to the occurrence of rainbow unevenness.

The present inventors have intensively studied to attain the aboveobject, and as a result, they have found that the combined use of aspecific backlight light source and a polyester film having a specificretardation makes it possible to solve the above problems, therebyleading to the completion of the present invention.

That is, the present invention includes the following inventions setforth in (1A) to (8A) and (1B) to (9B) below:

(1A) A liquid crystal display device comprising a backlight lightsource, and a liquid crystal cell disposed between two polarizers;

the backlight light source being a white light-emitting diode;

each of the polarizers comprising a polarizing film and protective filmslaminated on both sides of the polarizing film; and

at least one of the protective films being a polyester film having aretardation of 3,000 to 30,000 nm.

(2A) The liquid crystal display device as described above, wherein onepolarizer is disposed on a light-incoming side of the liquid crystalcell, and the other polarizer is disposed on a light-outgoing side ofthe liquid crystal cell, and the protective film on a light-outgoingside of the polarizing film of the polarizer disposed on thelight-outgoing side of the liquid crystal cell is a polyester filmhaving a retardation of 3,000 to 30,000 nm.

(3A) The liquid crystal display device as described above, wherein thepolyester film has a ratio of retardation to thickness-directionretardation (Re/Rth) of 0.2 or more.

(4A) A polarizer for use in a liquid crystal display device comprising awhite light-emitting diode as a backlight light source;

the polarizer comprising a polarizing film and protective filmslaminated on both sides of the polarizing film; and

at least one of the protective films being a polyester film having aretardation of 3,000 to 30,000 nm.

(5A) A protective film for a polarizer used in a liquid crystal displaydevice comprising a white light-emitting diode as a backlight lightsource;

the film comprising a polyester film having a retardation of 3,000 to30,000 nm.

(6A) The protective film as described above, wherein the polyester filmhas a ratio of retardation to thickness-direction retardation (Re/Rth)of 0.200 or more.

(7A) The protective film as described above, wherein the polyester filmhas an adhesion-facilitating layer.

(8A) The protective film as described above, wherein the polyester filmcomprises at least three or more layers, contains an ultravioletabsorber in the layer other than the outermost layers, and has a lighttransmittance at 380 nm of 20% or less.

(1B) A liquid crystal display device comprising a backlight lightsource, and a liquid crystal cell disposed between two polarizers;

the backlight light source being a white light-emitting diode;

each of the polarizers comprising a polarizing film and protective filmslaminated on both sides of the polarizing film; and

at least one of the protective films being a polyester film having aretardation of 3,000 to 30,000 nm.

(2B) The liquid crystal display device according to 1B, wherein theprotective film on a light-outgoing side of the polarizing film of thepolarizer disposed on a light-outgoing side with respect to the liquidcrystal cell is a polyester film having a retardation of 3,000 to 30,000nm.

(3B) The liquid crystal display device according to 1B or 2B, whereinthe polyester film has a ratio of retardation to thickness-directionretardation (Re/Rth) of 0.2 or more and 1.2 or less.

(4B) The liquid crystal display device according to any one of 1B to 3B,wherein the white light-emitting diode comprises a blue LED element anda yellow phosphor.

(5B) A polarizer for use in a liquid crystal display device comprising awhite light-emitting diode as a backlight light source;

the polarizer comprising a polarizing film and protective filmslaminated on both sides of the polarizing film; and

at least one of the protective films being a polyester film having aretardation of 3,000 to 30,000 nm.

(6B) A protective film for a polarizer used in a liquid crystal displaydevice comprising a white light-emitting diode as a backlight lightsource;

the film comprising a polyester film having a retardation of 3,000 to30,000 nm.

(7B) The protective film according to 6B, wherein the polyester film hasa ratio of retardation to thickness-direction retardation (Re/Rth) of0.2 or more.

(8B) The protective film according to 6B or 7B, wherein the polyesterfilm has an adhesion-facilitating layer.

(9B) The protective film according to any one of 6B to 8B, wherein thepolyester film comprises at least three or more layers, contains anultraviolet absorber in the layer other than the outermost layers, andhas a light transmittance at 380 nm of 20% or less.

Advantageous Effects of Invention

The liquid crystal display device, polarizer, and protective film of thepresent invention allows the transmitted light to have a spectrumapproximated to that of the light source at any observation angle, andensures excellent visibility without rainbow unevenness. Moreover, in apreferred embodiment, the protective film of the present invention hasmechanical strength suitable for making the film thinner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A and 1B are schematic drawings of embodiments of a liquidcrystal display device comprising a first polarizing film (1) and asecond polarizing film (1′) on opposite sides of a liquid crystal cell(3). FIG. 1A depicts a first oriented film (2) laminated on the firstpolarizing film (1) on the light-outgoing side of the liquid crystalcell, whereas FIG. 1B depicts a second oriented film (2′) laminated onthe second polarizing film (1′) on the light-incoming side of the liquidcrystal cell. A backlight source (4) is provided, and the liquid crystaldisplay device is viewed (5) on the light-outgoing side of the liquidcrystal cell.

FIG. 2 is a schematic drawing of an embodiment of a liquid crystaldisplay device comprising a first polarizing film (1) and a secondpolarizing film (1′) on opposite sides of a liquid crystal cell (3). Afirst oriented film (2) is laminated on the first polarizing film (1) onthe light-outgoing side of the liquid crystal cell, and a secondoriented film (2′) is laminated on the second polarizing film (1′) onthe light-incoming side of the liquid crystal cell. A backlight source(4) is provided and the liquid crystal display device is viewed (5) onthe light-outgoing side of the liquid crystal cell.

DESCRIPTION OF EMBODIMENTS

In general, a liquid crystal panel comprises a back module, a liquidcrystal cell, and a front module in this order, starting from the sideopposing a backlight light source to the side on which an image isdisplayed (i.e., the viewing side). The back module and the front moduleeach ordinarily include a transparent substrate, a transparentconductive film formed on the surface of the transparent substrate onthe liquid crystal cell side, and a polarizer disposed on the oppositeside. In this regard, the polarizer in the back module is disposed onthe side opposing the backlight light source, and the polarizer in thefront module is disposed on the side on which an image is displayed(i.e., the viewing side).

The liquid crystal display device of the present invention comprises, ascomponents, at least a backlight light source, and a liquid crystal celldisposed between two polarizers. Furthermore, the liquid crystal displaydevice may appropriately comprise, in addition to the above components,other components, such as a color filter, a lens film, an opticaldiffusion sheet, and an antireflection film.

The structure of the backlight may be an edge-light system comprising alight guide plate, a reflector, etc., as components, or a directunder-light system; however, in the present invention, it is necessaryto use white light-emitting diodes (white LEDs) as the backlight lightsource of the liquid crystal display device. In the present invention,the white LEDs refer to phosphor-based devices, that is, devices thatemit white light by the combined use of phosphors with light-emittingdiodes using compound semiconductors to emit blue light or ultravioletlight. Usable phosphors are yttrium-aluminum-garnet yellow phosphors,terbium-aluminum-garnet yellow phosphors, etc. Among these phosphors,white light-emitting diodes comprising light-emitting devices obtainedby the combined use of yttrium-aluminum-garnet yellow phosphors withblue light-emitting diodes using compound semiconductors are suitable asthe backlight light source of the present invention because of theircontinuous and wide emission spectrum and excellent luminous efficiency.Continuous emission spectrum means that there is no wavelength at whichthe light intensity is zero, at least in the visible light region.Furthermore, the method of the present invention enables a wide range ofapplications of white LEDs, which consume low power; therefore, it canalso attain the effect of energy conservation.

In relation to this, a type of LED that utilizes the combination ofred-emitting, green-emitting, and blue-emitting LEDs as a white lightsource (three-color LED system) has also been put to practical use.However, this method is not preferred, because it provides a narrow anddiscontinuous emission spectrum; therefore, it is expected to bedifficult to obtain the desired effect of the present invention.

In addition, fluorescent tubes, such as cold-cathode tubes andhot-cathode tubes, which have hitherto been widely used as backlightlight sources, only have a discontinuous emission spectrum with peaks atspecific wavelengths; therefore, it is difficult to obtain the desiredeffect of the present invention.

The polarizer has a structure in which a polarizing film prepared bydyeing PVA, etc., with iodine is bonded between two protective films.The present invention is characterized by using a polyester film havinga specific range of retardation as at least one of the protective films,which constitute the polarizer.

The mechanism for preventing the occurrence of rainbow unevenness by theabove embodiment is considered to be as follows.

When a polyester film having birefringent properties is disposed on oneside of the polarizing film, linearly polarized light emitted from thepolarizing film is disturbed when passing through the polymer film. Thetransmitted light shows an interference color specific to theretardation of the polymer film, which is the product of thebirefringence and the thickness thereof. Accordingly, when cold-cathodetubes, hot-cathode tubes, or the like that have a discontinuous emissionspectrum are used as the light source, the intensity of the transmittedlight varies depending on the wavelength, causing rainbow unevenness(refer to pages 30 and 31 of Proceedings of 15th MicroopticsConference).

In contrast, white-light emitting diodes have a continuous and wideemission spectrum in the visible light region. Therefore, when focusingon the envelope curve shape of the interference color spectrum of lighttransmitted through a birefringent material, a spectrum similar to theemission spectrum of the light source can be obtained by controlling theretardation of the polyester film. It is thus considered that rainbowunevenness is not generated, and visibility is significantly improved,because the envelope curve shape of the interference color spectrum ofthe light transmitted through the birefringent material becomes similarto the emission spectrum of the light source.

As described above, since the present invention uses white-lightemitting diodes having a wide emission spectrum as the light source, theenvelope curve shape of the spectrum of the transmitted light can beapproximated to the emission spectrum of the light source with only arelatively simple structure.

To attain the above effect, the polyester film used as the protectivefilm preferably has a retardation of 3,000 to 30,000 nm. If a polyesterfilm having a retardation of less than 3,000 nm is used as theprotective film, a strong interference color is presented when observedfrom an oblique direction. This makes the envelope curve shapedissimilar to the emission spectrum of the light source; therefore,excellent visibility cannot be ensured. The lower limit of theretardation is preferably 4,500 nm, more preferably 5,000 nm, still morepreferably 6,000 nm, even still more preferably 8,000 nm, and furtherstill more preferably 10,000 nm.

On the other hand, the upper limit of the retardation is 30,000 nm. Apolyester film having a retardation of higher than 30,000 nm is notpreferred. This is because the use of such a polyester film cannotsubstantially attain the effect of further improving visibility, whilealso leading to a considerable increase in the thickness of the film.This reduces the handling ability of the film as an industrial material.

In this connection, the retardation of the present invention can bedetermined by measuring refractive indices in two mutually orthogonaldirections and thickness, or can also be determined using a commerciallyavailable automatic birefringence analyzer, such as KOBRA-21ADH (OjiScientific Instruments).

The present invention is characterized in that at least one of theprotective films has the above specific retardation. The position of theprotective film having the specific retardation is not particularlylimited; however, in the case of a liquid crystal display devicecomprising a polarizer disposed on the light-incoming side (light sourceside), a liquid crystal cell, and a polarizer disposed on thelight-outgoing side (viewing side), it is preferable that the protectivefilm on the light-incoming side of the polarizing film of the polarizerdisposed on the light-incoming side, or the protective film on thelight-outgoing side of the polarizing film of the polarizer disposed onthe light-outgoing side is a polyester film having the specificretardation. See FIGS. 1A, 1B, and 2. In a particularly preferredembodiment, the protective film on the light-outgoing side of thepolarizing film of the polarizer disposed on the light-outgoing side isa polyester film having the specific retardation. If the polyester filmis disposed in a position other than the above-described positions, thepolarization properties of the liquid crystal cell may be changed. Sinceit is not preferable to use the polymer film of the present invention ina place for which polarization properties are required, the polymer filmof the present invention is preferably used as the protective film ofthe polarizer in such a specific position.

The polarizer of the present invention has a structure in which apolarizing film prepared by dyeing polyvinyl alcohol (PVA), etc., withiodine is bonded between two protective films, either of whichcharacteristically has the above specific retardation. The otherprotective film is preferably a birefringence-free film, typified by TACfilms, acrylic films, and norbornene films.

In another preferred embodiment, the surface of the polarizer used inthe present invention is coated with various hard coatings so as toprevent background reflections, glare, scratches, and so on.

The polyester used in the present invention may be polyethyleneterephthalate or polyethylene naphthalate, but may contain othercopolymerization components. The resins of these materials haveexcellent transparency, and also have excellent thermal and mechanicalproperties. This makes it possible to easily control the retardation bystretching treatment. In particular, polyethylene terephthalate is themost suitable material, because it has high intrinsic birefringence, andtherefore can relatively easily provide great retardation, even if thethickness of the film is small.

Moreover, in order to prevent degradation of the optical functional dye,such as iodine dye, the protective film of the present inventionpreferably has a light transmittance at a wavelength of 380 nm of 20% orless. The light transmittance at 380 nm is more preferably 15% or less,still more preferably 10% or less, and particularly preferably 5% orless. When the above light transmittance is 20% or less, the degradationof the optical functional dye caused by ultraviolet light can beprevented. In addition, the transmittance in the present invention ismeasured vertically with respect to the plane of the film, and can bemeasured with a spectrophotometer (e.g., Hitachi U-3500spectrophotometer).

In order to adjust the transmittance of the protective film of thepresent invention at a wavelength of 380 nm to 20% or less, it ispreferable to suitably control the type and concentration of theultraviolet absorber, and the thickness of the film. The ultravioletabsorber used in the present invention is a known substance. Examples ofthe ultraviolet absorber include organic ultraviolet absorbers andinorganic ultraviolet absorbers; however, organic ultraviolet absorbersare preferred in terms of transparency. Specific examples of organicultraviolet absorbers include benzotriazole-based ultraviolet absorbers,benzophenone-based ultraviolet absorbers, cyclic imino ester-basedultraviolet absorbers, and a combination thereof; however, the organicultraviolet absorbers are not particularly limited as long as they havean absorbance within the range specified in the present invention.However, benzotriazole-based ultraviolet absorbers and cyclic iminoester-based ultraviolet absorbers are particularly preferred in terms ofdurability. When two or more ultraviolet absorbers are used incombination, ultraviolet lights of different wavelengths can be absorbedat the same time. Thus, the ultraviolet absorption effect can be furtherimproved.

Examples of benzophenone-based ultraviolet absorbers,benzotriazole-based ultraviolet absorbers, and acrylonitrile-basedultraviolet absorbers include2-[2′-hydroxy-5′-(methacryloyloxymethyl)phenyl]-2H-benzotriazole,2-[2′-hydroxy-5′-(methacryloyloxyethyl)phenyl]-2H-benzotriazole,2-[2′-hydroxy-5′-(methacryloyloxypropyl)phenyl]-2H-benzotriazole,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone,2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol,2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole,2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl-6-(tert-butyl)phenol,2,2′-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol),etc. Examples of cyclic imino ester-based ultraviolet absorbers include2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one),2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one,2-phenyl-3,1-benzoxazin-4-one, etc. However, ultraviolet absorbers arenot limited to these examples.

In another preferred embodiment, in addition to the ultravioletabsorber, various additives other than catalysts are added in the rangewhere the effect of the present invention is not impaired. Examples ofsuch additives include inorganic particles, heat-resistant polymerparticles, alkali metal compounds, alkaline earth metal compounds,phosphorus compounds, antistatic agents, light-resistant agents, flameretardants, heat stabilizers, antioxidants, anti-gelling agents,surfactants, etc. Moreover, in order to achieve high transparency, it isalso preferable that the polyester film does not substantially containparticles. “Not substantially contain particles” indicates that, forexample, in the case of inorganic particles, the content of inorganicelements quantified by X-ray fluorescence analysis is 50 ppm or less,preferably 10 ppm or less, and particularly preferably not greater thanthe detection limit.

Furthermore, in order to enhance the adhesion of the polyester film ofthe present invention to the polarizing film, the polyester film can besubjected to corona treatment, coating treatment, flame treatment, orthe like.

In the present invention, in order to improve the adhesion of the filmof the present invention to the polarizing film, the film of the presentinvention preferably has, on at least one side thereof, anadhesion-facilitating layer comprising at least one of polyester resin,polyurethane resin, and polyacrylic resin as a main component. The “maincomponent” as used herein refers to, among solid components thatconstitute the adhesion-facilitating layer, one with 50 mass % or more.The coating solution used to form the adhesion-facilitating layer of thepresent invention is preferably an aqueous coating solution comprisingat least one of water-soluble or water-dispersible copolymerizedpolyester resin, acrylic resin, and polyurethane resin. Examples of suchcoating solutions include a water-soluble or water-dispersiblecopolymerized polyester resin solution, acrylic resin solution,polyurethane resin solution, etc., as disclosed in JP 3567927 B, JP3589232 B, JP 3589233 B, JP 3900191 B, JP 4150982 B, etc.

The adhesion-facilitating layer can be obtained by applying the coatingsolution to one side or both sides of a longitudinally uniaxiallystretched film, followed by drying at 100 to 150° C., and furtherstretching the film in a transverse direction. The final amount ofcoating of the adhesion-facilitating layer is preferably maintained inthe range of 0.05 to 0.20 g/m². When the amount of coating is less than0.05 g/m², the resulting adhesion to the polarizing film may beinsufficient. In contrast, when the amount of coating exceeds 0.20 g/m²,blocking resistance may be reduced. When the adhesion-facilitating layeris provided on both sides of the polyester film, the amounts of coatingof the adhesion-facilitating layers on both sides may be the same ordifferent, and can be independently set within the above range.

It is preferable to add particles to the adhesion-facilitating layer soas to impart lubricating properties. Fine particles having an averageparticle diameter of 2 μm or less are preferably used. Particles havingan average particle diameter of more than 2 μm tend to be easily droppedout from the coating layer. Examples of the particles to be added to theadhesion-facilitating layer include inorganic particles of titaniumoxide, barium sulfate, calcium carbonate, calcium sulfate, silica,alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite,zirconia, tungsten oxide, lithium fluoride, calcium fluoride, or thelike; and styrene, acrylic, melamine, benzoguanamine, silicone, andother organic polymer particles. These particles may be added singly orin combination to the adhesion-facilitating layer.

Moreover, the method for applying the coating solution may be a knownmethod. Examples thereof include reverse-roll coating, gravure coating,kiss coating, roll-brush coating, spray coating, air-knife coating,wire-bar coating, pipe doctor method, and the like. These methods can beused singly or in combination.

The average particle diameter of the above particles is measured in thefollowing manner.

Images of the particles are taken by a scanning electron microscope(SEM). The maximum diameter of 300 to 500 individual particles (distancebetween the most separated two points) is measured at such amagnification that the size of the smallest single particle is 2 to 5mm. The average of the maximum diameter of the particles is regarded asthe average particle diameter.

The polyester film, which is used as the protective film of the presentinvention, can be produced by a general production method of polyesterfilms. For example, non-oriented polyester obtained by melting apolyester resin and extruding the molten resin into a sheet-like shapeis stretched in a longitudinal direction through the use of rollvelocity difference at a temperature higher than the glass transitiontemperature, and then stretched in a transverse direction with a tenter,followed by heat treatment.

The polyester film of the present invention may be a uniaxiallystretched film or a biaxially stretched film. However, care should betaken when a biaxially stretched film is used as the protective film,because no rainbow unevenness is observed when the film is viewed fromright above the film plane, whereas rainbow unevenness may be observedwhen the film is viewed from an oblique direction.

This phenomenon is caused by the following factors: The biaxiallystretched film has an index ellipsoid with different refractive indicesin the running direction, width direction, and thickness direction, andthere is a direction in which the retardation is zero (the indexellipsoid looks like a perfect circle) depending on the lighttransmission direction in the film. Accordingly, when the screen of theliquid crystal display is observed from a specific oblique direction,there may be a point at which the retardation is zero. Centering on thatpoint, rainbow unevenness is generated in a concentric manner.

When the angle between the position right above the film surface (normaldirection) and the position at which rainbow unevenness is visible isregarded as θ, the angle θ becomes larger as the birefringence in thefilm plane is greater, and rainbow unevenness is less likely to bevisible. Since a biaxially stretched film tends to have a lower angle θ,a uniaxially stretched film, in which rainbow unevenness is less likelyto be visible, is preferred.

However, a complete uniaxial (uniaxially symmetric) film is notpreferred, because mechanical strength in a direction orthogonal to theorientation direction remarkably decreases. In the present invention, itis preferable to have biaxiality (biaxial symmetry) in a range whererainbow unevenness is not substantially generated, or in a range whererainbow unevenness is not generated within the range of the viewingangle required for liquid crystal display screens.

As the means for preventing the occurrence of rainbow unevenness whilemaintaining the mechanical strength of the protective film, the presentinventors found controlling the ratio of retardation (in-planeretardation) and thickness-direction retardation (Rth) of the protectivefilm in a specific range. A thickness-direction phase differenceindicates the average of phase differences obtained by multiplying eachof two birefringence values ΔNxz and ΔNyz, when the film is viewed fromthe thickness-direction cross-section, by the film thickness d. Thesmaller the difference between the in-plane retardation and thethickness-direction retardation, the higher the isotropy of the actionof birefringence depending on the observation angle. Thus, the variationof retardation due to the observation angle is reduced. Accordingly,rainbow unevenness due to the observation angle is less likely to begenerated.

The ratio of retardation to thickness-direction retardation (Re/Rth) ofthe polyester film of the present invention is preferably 0.200 orhigher, more preferably 0.500 or higher, and still more preferably 0.600or higher. The greater the ratio of retardation to thickness-directionretardation (Re/Rth), the higher the isotropy of the action ofbirefringence, and the less likely the occurrence of rainbow unevennessdepending on the observation angle. A complete uniaxial (uniaxiallysymmetric) film has a ratio of retardation to thickness-directionretardation (Re/Rth) of 2.0. However, as described above, as the filmbecomes closer to a complete uniaxial (uniaxially symmetric) film,mechanical strength in a direction orthogonal to the orientationdirection remarkably decreases.

On the other hand, the ratio of retardation to thickness-directionretardation (Re/Rth) of the polyester film of the present invention ispreferably 1.2 or less, and more preferably 1.0 or less. In order tocompletely prevent the occurrence of rainbow unevenness depending on theobservation angle, the above ratio of retardation to thickness-directionretardation (Re/Rth) is not necessarily 2.0, but is sufficiently 1.2 orless. Moreover, even if the above ratio is 1.0 or less, it issufficiently possible to satisfy viewing-angle characteristics requiredfor liquid crystal display devices (right and left viewing angle: about180, and upper and lower viewing angle: about 120).

The film-forming conditions of the polyester film of the presentinvention are described in detail below. The temperature for stretchingin the longitudinal direction and the temperature for stretching in thetransverse direction are preferably 80 to 130° C., and particularlypreferably 90 to 120° C. The stretch ratio for stretching in thelongitudinal direction is preferably 1.0 to 3.5, and particularlypreferably 1.0 to 3.0. The stretch ratio for stretching in thetransverse direction is preferably 2.5 to 6.0, and particularlypreferably 3.0 to 5.5. In order to control the retardation within theabove range, it is preferable to control the proportion of longitudinalstretch ratio and transverse stretch ratio. An overly small differencebetween the longitudinal and transverse stretch ratios is not preferred,because it is difficult to increase the retardation. To increase theretardation, it is also preferable to set the stretch temperature tolow. In the subsequent heat treatment, the treatment temperature ispreferably 100° C. to 250° C., and particularly preferably 180° C. to245° C.

In order to suppress variation of the retardation, the thicknessvariation of the film is preferably low. Since the stretch temperatureand the stretch ratios have a great influence on the film thicknessvariation, it is necessary to optimize the film production conditions interms of the thickness variation. In particular, when the longitudinalstretch ratio is reduced to increase the retardation, the longitudinalthickness variation may deteriorate. Since there is an area in which thelongitudinal thickness variation significantly deteriorates in aspecific range of the stretch ratio, it is preferable to determine thefilm production conditions outside that range.

The film of the present invention preferably has a thickness variationof 5.0% or less, more preferably 4.5% or less, still more preferably4.0% or less, and particularly preferably 3.0% or less.

As described above, it is possible to control the retardation of thefilm in a specific range by appropriately setting the stretch ratio, thestretch temperature, and the thickness of the film. For example, thehigher the stretch ratio, the lower the stretch temperature, or thegreater the thickness of the film, the more likely a great retardationis obtained. In contrast, the lower the stretch ratio, the higher thestretch temperature, or the smaller the thickness of the film, the morelikely a small retardation is obtained. However, when the film thicknessis increased, the phase difference in the thickness direction is likelyto increase. It is therefore preferable to appropriately set the filmthickness in the range described later. In addition to the control ofretardation, it is necessary to determine the final film productionconditions in consideration of physical properties, etc., required forprocessing.

The polyester film used in the present invention may have any thickness,but preferably has a thickness in the range of 15 to 300 μm, and morepreferably 15 to 200 μm. Even a film having a thickness of lower than 15μm can, in principle, provide a retardation of 3,000 nm or higher. Inthis case, however, the mechanical properties of the film becomesignificantly anisotropic. This causes the film to, for example, tear orbreak, which significantly reduces the practicality of the film as anindustrial material. The lower limit of the thickness is particularlypreferably 25 μm. On the other hand, when the upper limit of thethickness of the protective film exceeds 300 μm, the polarizer is overlythick, which is not preferred. The upper limit of the thickness ispreferably 200 μm in terms of the practicality as the protective film.The upper limit of the thickness is particularly preferably 100 μm,which is almost equivalent to the thickness of a general TAC film. Inorder to control the retardation in the range of the present inventionin the above thickness range, polyethylene terephthalate is preferred asthe polyester used as the film base.

Moreover, as the method of mixing an ultraviolet absorber with thepolyester film of the present invention, known methods can be used incombination. For example, a masterbatch is previously produced by mixinga dried ultraviolet absorber with polymer raw materials using a kneadingextruder, and the masterbatch and the polymer raw materials are mixedduring the film production.

In that case, the ultraviolet absorber concentration in the masterbatchis preferably 5 to 30 mass % so as to uniformly disperse andeconomically mix the ultraviolet absorber. Preferred conditions forproducing the masterbatch include use of a kneading extruder, andextrusion at a temperature equal to or greater than the melting point ofthe polyester raw material and equal to or lower than 290° C. for 1 to15 minutes. At a temperature of 290° C. or more, a large amount ofultraviolet absorber is lost, and the viscosity of the masterbatch issignificantly reduced. For an extrusion time of 1 minute or less, it isdifficult to homogeneously mix the ultraviolet absorber. At this point,a stabilizer, a color tone-controlling agent, and an antistatic agentmay be added, if necessary.

Furthermore, in the present invention, it is preferable that the filmhas a multi-layered structure including at least three or more layers,and that an ultraviolet absorber is added to the intermediate layer(s)of the film. Such a three-layer film containing an ultraviolet absorberin the intermediate layer can be specifically produced in the followingmanner. Polyester pellets are singly used for the outer layers. For theintermediate layer, polyester pellets and a masterbatch containing anultraviolet absorber are mixed in a predetermined proportion, and thendried. These are supplied into a known extruder for melt-lamination, andextruded through a slit-shaped die into a sheet-like shape, followed bycooling and solidification on a casting roll, thereby forming anunstretched film. More specifically, film layers constituting both outerlayers and a film layer constituting the intermediate layer arelaminated by using two or more extruders, a three-layer manifold, or ajunction block (e.g., a junction block having a square-shaped junction).A three-layered sheet is extruded through a die and cooled on a castingroll, thereby forming an unstretched film. In the invention, in order toremove foreign substances, which cause optical defects, from the rawmaterial (i.e., polyester), it is preferable to perform high-precisionfiltration during melt extrusion. The filtration particle size (initialfiltration efficiency: 95%) of a filtering medium used forhigh-precision filtration of the molten resin is preferably 15 μm orless. When the filtration particle size of the filtering medium is morethan 15 μm, removal of foreign substances having a size of 20 μm or moreis likely to be insufficient.

EXAMPLES

The present invention will hereinafter be described more specifically byway of Examples; however, the present invention is not limited to theExamples described below. The present invention can be put into practiceafter appropriate modifications or variations within a range meeting thegist of the present invention, all of which are included in thetechnical scope of the present invention. In the following Examples, themethods for the evaluation of physical properties are as follows:

(1) Retardation (Re)

A retardation is a parameter defined by the product (ΔNxy×d) of theanisotropy (ΔNxy=|Nx−Ny|) of the refractive indices in two mutuallyorthogonal directions on a film and the film thickness d (nm), and is ascale indicating optical isotropy or anisotropy. The anisotropy (ΔNxy)of refractive indices in two directions is obtained by the followingmethod. The directions of orientation axes of a film were determinedusing two polarizers, and the film was cut into a 4 cm×2 cm rectangle sothat the direction of the orientation axe was orthogonal to either sideof the rectangle. The cut piece was used as a sample for measurement.

The sample was measured for the refractive indices (Nx and Ny) in twomutually orthogonal directions and the refractive index (Nz) in thethickness direction by the use of an Abbe refractometer (NAR-4Tavailable from Atago Co., Ltd.; measurement wavelength: 589 nm). Then,the absolute value (|Nx−Ny|) of the difference between the refractiveindices in two directions was defined as the anisotropy (ΔNxy) of therefractive indices. The film thickness d (nm) was measured using anelectric micrometer (Millitron 1245D, available from Feinpruf GmbH), andwas converted to nm units. The retardation (Re) was determined by theproduct (ΔNxy×d) of the anisotropy ((ΔNxy) of the refractive indices andthe film thickness d (nm).

(2) Thickness-Direction Retardation (Rth)

A thickness-direction retardation is a parameter indicating the averageof retardation obtained by multiplying two birefringence values ΔNxz(=|Nx−Nz|) and ΔNyz (=|Ny−Nz|) when viewed from a film-thicknessdirection cross-section, by a film thickness d. The refractive indicesNx, Ny, and Nz, and the film thickness d (nm) were determined in thesame manner as in the measurement of retardation, and the average valueof (ΔNxz×d) and (ΔNyz×d) was calculated to determine thethickness-direction retardation (Rth).

(3) Light Transmittance at Wavelength of 380 nm

Using a spectrophotometer (U-3500, produced by Hitachi, Ltd.), the lighttransmittance of each film at a wavelength of 300 to 500 nm was measuredusing the air space as standard, and the light transmittance at awavelength of 380 nm was determined.

(4) Observation of Rainbow Unevenness

A polyester film produced by the method described below was bonded toone side of a polarizing film comprising PVA and iodine so that theabsorption axis of the polarizing film was vertical to the mainorientation axis of the polyester film. A TAC film (produced by FujifilmCorporation; thickness: 80 μm) was bonded to the opposite side, therebyproducing a polarizer. The obtained polarizer was placed on thelight-outgoing side of a liquid crystal display device that employed, asa light source, white LEDs (NSPW500CS, available from NichiaCorporation) having light-emitting devices obtained by the combined useof yttrium-aluminum-garnet yellow phosphors with blue light-emittingdiodes, so that the polyester film was disposed on the viewing side. Theliquid crystal display device had a polarizer comprising two TAC filmsas protective films on the light-incoming side of the liquid crystalcell. The polarizer of the liquid crystal display device was visuallyobserved from the front direction and an oblique direction, and theoccurrence of rainbow unevenness was determined as follows.

In Comparative Example 3, a backlight light source using cold-cathodetubes as the light source was used in place of the white LEDs.

++: no formation of rainbow unevenness observed from any direction.

+: partial, very light rainbow unevenness observed from an obliquedirection

−: clear rainbow unevenness observed from an oblique direction

(5) Tear Strength

The tear strength of each film was measured according to JIS P-8116using an Elmendorf tearing tester (produced by Toyo Seiki Seisaku-sho,Ltd.). The tear direction was parallel to the orientation axis directionof the film, and the results were evaluated as follows. The orientationaxis direction was measured by a molecular orientation analyzer(MOA-6004, produced by Oji Scientific Instruments).

+: Tear strength was 50 mN or more.

−: Tear strength was less than 50 mN.

Production Example 1: Polyester A

The temperature of an esterification reaction vessel was raised, andwhen the temperature reached 200° C., 86.4 parts by mass of terephthalicacid and 64.6 parts by mass of ethylene glycol were put in the vessel.While stirring the mixture, 0.017 parts by mass of antimony trioxide,0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts bymass of triethylamine were added as catalysts. Subsequently, thepressure and temperature were raised, and pressure esterification wasperformed at a gage pressure of 0.34 MPa at 240° C. Then, the pressurein the esterification reaction vessel was returned to normal pressure,and 0.014 parts by mass of phosphoric acid was added. Further, thetemperature was raised to 260° C. over 15 minutes, and 0.012 parts bymass of trimethyl phosphate was added. Subsequently, after 15 minutes,dispersion was performed with a high-pressure disperser. After 15minutes, the obtained esterification reaction product was transferred toa polycondensation reaction vessel, and a polycondensation reaction wasperformed at 280° C. under reduced pressure.

After completion of the polycondensation reaction, filtration wasperformed using a Naslon filter (95% cut size: 5 μm). The resultant wasextruded through a nozzle into a strand shape, cooled and solidifiedwith cooling water, which had been previously filtered (pore size: 1 μmor less), and cut into pellets. The obtained polyethylene terephthalateresin (A) had an intrinsic viscosity of 0.62 dl/g, and did notsubstantially contain inert particles and internally deposited particles(hereafter abbreviated as “PET (A)”).

Production Example 2: Polyester B

A dried ultraviolet absorber(2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) (10 parts by mass)and 90 parts by mass of particle-free PET (A) (intrinsic viscosity: 0.62dl/g) were mixed, and a kneading extruder was used to obtain apolyethylene terephthalate resin (B) containing the ultraviolet absorber(hereafter abbreviated as “PET (B)”).

Production Example 3: Preparation of Adhesion-Modified Coating Solution

A transesterification reaction and a polycondensation reaction wereperformed in a standard manner to prepare a water-dispersible sulfonicacid metal salt group-containing copolymerized polyester resincomprising, as dicarboxylic acid components (based on the entiredicarboxylic acid components), 46 mol % of terephthalic acid, 46 mol %of isophthalic acid, and 8 mol % of sodium 5-sulfonatoisophthalate; andas glycol components (based on the entire glycol components), 50 mol %of ethylene glycol and 50 mol % of neopentyl glycol. Subsequently, 51.4parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 partsby mass of n-butyl cellosolve, and 0.06 parts by mass of nonionicsurfactant were mixed, and then stirred under heating. When thetemperature reached 77° C., 5 parts by mass of the abovewater-dispersible sulfonic acid metal salt group-containingcopolymerized polyester resin was added, and continuously stirred untilthe mass of the resin disappeared. Thereafter, the resulting resinaqueous dispersion was cooled to room temperature, thereby obtaining ahomogeneous water-dispersible copolymerized polyester resin solutionhaving a solids content of 5.0 mass %. Furthermore, 3 parts by mass ofaggregate silica particles (Sylysia 310, produced by Fuji SilysiaChemical Ltd.) was dispersed in 50 parts by mass of water. Then, 0.54parts by mass of the water dispersion of Sylysia 310 was added to 99.46parts by mass of the above water-dispersible copolymerized polyesterresin solution. While stirring the mixture, 20 parts by mass of waterwas added, thereby obtaining an adhesion-modified coating solution.

Example 1

As the starting materials for the base film intermediate layer, 90 partsby mass of particle-free PET (A) resin pellets and 10 parts by mass ofultraviolet absorber-containing PET (B) resin pellets were vacuum-dried(1 Torr) at 135° C. for 6 hours, and then supplied to an extruder 2 (forthe intermediate layer II). Further, PET (A) was dried by a standardmethod, supplied to extruders 1 (each for the outer layer I and theouter layer III), and melted at 285° C. These two polymers were eachfiltered through a filtering medium of a stainless steel sintered body(nominal filtering accuracy: 10 μm-particle 95% cut), laminated by twotypes of three-layered junction blocks, and extruded through a die intoa sheet-like shape. The resulting sheet was cooled and solidified bywinding the sheet around a casting drum having a surface temperature of30° C. by an electrostatic casting method, thereby forming anunstretched film. At this time, the discharge of each extruder wasadjusted so that the thickness ratio of layer I, layer II, and layer IIIwas 10:80:10.

Then, the above-prepared adhesion-modified coating solution was appliedto both sides of the unstretched PET film by reverse-roll coating sothat the amount of dried coating was 0.08 g/m², followed by drying at80° C. for 20 seconds.

The unstretched film, on which a coating layer had been formed, wasguided to a tenter stretching machine. While holding the edges of thefilm with clips, the film was guided to a hot-air zone with atemperature of 125° C., and stretched 4.0 times in the width direction.Subsequently, while maintaining the width of the film stretched in thewidth direction, the film was treated at a temperature of 225° C. for 30seconds, and further subjected to 3% relaxation treatment in the widthdirection. Thus, a uniaxially oriented PET film having a thickness ofabout 50 μm was obtained.

Example 2

A uniaxially oriented PET film having a thickness of about 100 μm wasobtained in the same manner as in Example 1, except that the thicknessof the unstretched film was changed.

Example 3

An unstretched film produced in the same manner as in Example 1 washeated to 105° C. using heated rolls and an infrared heater. Thereafter,the film was stretched 1.5 times in the running direction by rollshaving different peripheral speeds, and then stretched 4.0 times in thewidth direction in the same manner as in Example 1, thereby obtaining abiaxially oriented PET film having a thickness of about 50 μm.

Example 4

An unstretched film was stretched 2.0 times in the running direction and4.0 times in the width direction in the same manner as in Example 3,thereby obtaining a biaxially oriented PET film having a thickness ofabout 50 μm.

Example 5

An unstretched film was stretched 3.3 times in the running direction and4.0 times in the width direction in the same manner as in Example 3,thereby obtaining a biaxially oriented PET film having a thickness ofabout 75 μm.

Example 6

A uniaxially oriented PET film having a thickness of 50 μm was obtainedin the same manner as in Example 1, without using the ultravioletabsorber-containing PET resin (B) in the intermediate layer. Theobtained film did not have rainbow unevenness, but had high lighttransmittance at 380 nm, which may degrade the optical functional dye.

Example 7

An unstretched film was stretched 4.0 times in the running direction and1.0 time in the width direction in the same manner as in Example 3,thereby obtaining a uniaxially oriented PET film having a thickness ofabout 100 μm. The obtained film had a retardation of 3,000 nm or more.Although the visibility was excellent, the mechanical strength wasslightly inferior.

Example 8

An unstretched film was stretched 3.5 times in the running direction and3.7 times in the width direction in the same manner as in Example 3,thereby obtaining a biaxially oriented PET film having a thickness ofabout 250 μm. The obtained film had a retardation of 4,500 nm or more;however, the Re/Rth ratio was less than 0.2, and thus, very slightrainbow unevenness was observed when the film was viewed from an obliquedirection.

Example 9

An unstretched film was stretched 1.0 time in the running direction and3.5 times in the width direction in the same manner as in Example 1,thereby obtaining a uniaxially oriented PET film having a thickness ofabout 75 μm.

Example 10

A uniaxially oriented PET film having a thickness of about 275 μm wasobtained in the same manner as in Example 1, except that the thicknessof the unstretched film was changed.

Comparative Example 1

An unstretched film was stretched 3.6 times in the running direction and4.0 times in the width direction in the same manner as in Example 3,thereby obtaining a biaxially oriented PET film having a thickness ofabout 38 μm. The obtained film had a low retardation, and rainbowunevenness was observed when the film was viewed from an obliquedirection.

Comparative Example 2

A uniaxially oriented PET film having a thickness of about 10 μm wasobtained in the same manner as in Example 1, except that the thicknessof the unstretched film was changed.

The obtained film was very easy to tear and had no body. Therefore, thisfilm could not be used as the protective film. Moreover, retardation waslow, and rainbow unevenness was observed.

Comparative Example 3

The same procedure as in Example 1 was carried out, except that theobservation of rainbow unevenness was performed using cold-cathode tubesas the light source of the liquid crystal display device.

Table 1 below shows the results of the observation of rainbow unevennessand the measurement of tear strength of the polyester films of Examples1 to 10 and Comparative Examples 1 to 3.

TABLE 1 Running- Width- Observation 380-nm light Thickness directiondirection Re Rth Re/Rth of rainbow Tear transmittance (μm) stretch ratiostretch ratio Nx Ny Nz (nm) (nm) ratio unevenness strength (%) Ex. 1 501.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + 8.5 Ex. 2 100 1.0 4.01.594 1.696 1.513 10200 13233 0.771 ++ + 1.0 Ex. 3 50 1.5 4.0 1.6081.686 1.508 3915 6965 0.562 + + 8.5 Ex. 4 50 2.0 4.0 1.617 1.681 1.5023215 7341 0.438 + + 8.5 Ex. 5 75 3.3 4.0 1.640 1.688 1.498 3570 124800.286 + + 2.5 Ex. 6 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ +79.0 Ex. 7 100 4.0 1.0 1.735 1.570 1.520 16500 13250 1.245 ++ − 1.0 Ex.8 250 3.5 3.7 1.660 1.687 1.522 6750 37875 0.178 + + 0.4 Ex. 9 75 1.03.5 1.580 1.678 1.525 7350 7800 0.942 ++ + 2.5 Ex. 10 275 1.0 4.0 1.5931.697 1.513 28476 36314 0.784 ++ + 0.3 Comp. 38 3.6 4.0 1.649 1.6801.497 1178 6365 0.185 − + 15.0 Ex. 1 Comp. 10 1.0 4.0 1.591 1.698 1.5131070 1318 0.812 − − 56.0 Ex. 2 Comp. 50 1.0 4.0 1.593 1.697 1.513 51776602 0.784 − + 8.5 Ex. 3

In the observation of rainbow unevenness in the films of Examples 1 to10, as shown in Table 1, rainbow unevenness was not observed in anyfilms when the films were viewed from the front direction. When thefilms of Examples 3 to 5 and 8 were viewed from an oblique direction,rainbow unevenness was partially observed; whereas when the films ofExamples 1, 2, 6, 7, 9, and 10 were viewed from an oblique direction, norainbow unevenness was observed at all. In contrast, when the films ofComparative Examples 1 to 3 were viewed from an oblique direction,rainbow unevenness was clearly observed.

It was also demonstrated that the tear strength of the films of Example7 and Comparative Example 2 was not sufficient. The reason for this isconsidered to be because the film of Example 7 had an overly high Re/Rthratio, and the film of Comparative Example 2 had an overly low filmthickness.

INDUSTRIAL APPLICABILITY

The liquid crystal display device, polarizer, and protective film of thepresent invention are very highly industrially applicable, because theuse of them contributes to thinner LCDs and lower cost, withoutreduction in visibility caused by rainbow unevenness.

1. A display device comprising a first polarizer, a second polarizer, aliquid crystal cell, and a backlight source, wherein the liquid crystalcell has a light-outgoing side and a light-incoming side, the firstpolarizer is disposed on the light-outgoing side of the liquid crystalcell, the first polarizer comprises (a) a first polarizing film and (b)a first protective film laminated on the light-outgoing side of thefirst polarizing film, the second polarizer is disposed on thelight-incoming side of the liquid crystal cell, the second polarizercomprises (a) a second polarizing film and (b) a second protective filmlaminated on the light-incoming side of the second polarizing film, atleast one of the first protective film and the second protective film isan oriented film having an in-plane retardation of 3,215 to 30,000 nmand a ratio of in-plane retardation to thickness-direction retardation(Re/Rth) of 0.2 to 2.0, and no oriented film having an in-planeretardation of 3,215 to 30,000 nm is disposed between the light-incomingside of the first polarizing film and the light-outgoing side of thesecond polarizing film.
 2. The display device of claim 1, wherein one ofthe first protective film and the second protective film is not anoriented film having an in-plane retardation of 3,215 to 30,000 nm and aratio of in-plane retardation to thickness-direction retardation(Re/Rth) of 0.2 to 2.0.
 3. The display device of claim 2, wherein thefirst protective film or the second protective film that is not anoriented film having an in-plane retardation of 3,215 to 30,000 nm and aratio of in-plane retardation to thickness-direction retardation(Re/Rth) of 0.2 to 2.0 is a polyester film.
 4. The display device ofclaim 2, wherein the first protective film or the second protective filmthat is not an oriented film having an in-plane retardation of 3,215 to30,000 nm and a ratio of in-plane retardation to thickness-directionretardation (Re/Rth) of 0.2 to 2.0 is a triacetyl cellulose film, anacrylic film, or a norbornene film.
 5. The display device of claim 2,wherein the first protective film or the second protective film that isnot an oriented film having an in-plane retardation of 3,215 to 30,000nm and a ratio of in-plane retardation to thickness-directionretardation (Re/Rth) of 0.2 to 2.0 is a retardation-free film.
 6. Thedisplay device of claim 2, wherein the first protective film or thesecond protective film that is an oriented film having an in-planeretardation of 3,215 to 30,000 nm and a ratio of in-plane retardation tothickness-direction retardation (Re/Rth) of 0.2 to 2.0 is a polyesterfilm.
 7. The display device of claim 1, wherein the first protectivefilm is an oriented film having an in-plane retardation of 3,215 to30,000 nm and a ratio of in-plane retardation to thickness-directionretardation (Re/Rth) of 0.2 to 2.0.
 8. The display device of claim 7,wherein the first protective film that is an oriented film having anin-plane retardation of 3,215 to 30,000 nm and a ratio of in-planeretardation to thickness-direction retardation (Re/Rth) of 0.2 to 2.0 isa polyester film.
 9. The display device of claim 7, wherein the secondprotective film is not an oriented film having an in-plane retardationof 3,215 to 30,000 nm and a ratio of in-plane retardation tothickness-direction retardation (Re/Rth) of 0.2 to 2.0 and is apolyester film.
 10. The display device of claim 7, wherein the secondprotective film is not an oriented film having an in-plane retardationof 3,215 to 30,000 nm and a ratio of in-plane retardation tothickness-direction retardation (Re/Rth) of 0.2 to 2.0 and is atriacetyl cellulose film, an acrylic film, or a norbornene film.
 11. Thedisplay device of claim 7, wherein the second protective film is not anoriented film having an in-plane retardation of 3,215 to 30,000 nm and aratio of in-plane retardation to thickness-direction retardation(Re/Rth) of 0.2 to 2.0 and is a retardation-free film.
 12. The displaydevice of claim 1, wherein the second protective film is an orientedfilm having an in-plane retardation of 3,215 to 30,000 nm and a ratio ofin-plane retardation to thickness-direction retardation (Re/Rth) of 0.2to 2.0.
 13. The display device of claim 12, wherein the secondprotective film that is an oriented film having an in-plane retardationof 3,215 to 30,000 nm and a ratio of in-plane retardation tothickness-direction retardation (Re/Rth) of 0.2 to 2.0 is a polyesterfilm.
 14. The display device of claim 12, wherein the first protectivefilm is not an oriented film having an in-plane retardation of 3,215 to30,000 nm and a ratio of in-plane retardation to thickness-directionretardation (Re/Rth) of 0.2 to 2.0 and is a polyester film.
 15. Thedisplay device of claim 12, wherein the first protective film is not anoriented film having an in-plane retardation of 3,215 to 30,000 nm and aratio of in-plane retardation to thickness-direction retardation(Re/Rth) of 0.2 to 2.0 and is a triacetyl cellulose film, an acrylicfilm, or a norbornene film.
 16. The display device of claim 12, whereinthe first protective film is not an oriented film having an in-planeretardation of 3,215 to 30,000 nm and a ratio of in-plane retardation tothickness-direction retardation (Re/Rth) of 0.2 to 2.0 and is aretardation-free film.